The invention relates to a film which comprises at least one transparent replicating layer having a diffractive relief structure and a reflective layer, a method for the production of such a film and a use of the film.
Films of the type mentioned at the outset are known and are used for securing and decorating articles, documents, packagings and the like. Metallic or nonmetallic inorganic reflective layers are used in order optimally to accentuate an optically variable effect produced by the diffractive relief structure. Such an optically variable effect manifests itself in that an observer perceives different appearances of the film at different viewing angles, such as different color impressions and/or image motifs and/or characters and/or dullness. Inter alia, holograms, holographic displays with kinematic effects and the like are recognizable.
For specific fields of use, the known films have proved to be not very suitable since the optically variable effects produced are too striking, are too strongly reflective and/or irritate the human eye. This is the case, for example, with components in the interior of a motor vehicle which are present in the direct field of view of the driver, in the case of motor vehicle number plates or the case of pieces of furniture, packagings, certain valuable documents and the like.
For these applications, films which have other security features or decorative elements are therefore relied upon.
An example of use in the area of motor vehicle number plates, which however is substantially also applicable to the other abovementioned applications, is described in more detail below by way of illustration.
Motor vehicle number plates consist as a rule of a support plate, which usually consists of an aluminum or steel sheet. A raised character legend is embossed in the support plate by means of a mechanical embossing process. The character legend usually consists of alphanumeric characters, which, for example in Germany, indicate the place of registration of the motor vehicle, and form an individual number. In order to make the character legend of the embossed motor vehicle number plate readily visible, the raised embossed areas are provided with a colored coating. A corresponding ink transfer by means of a blocking film which consists of a substrate film which is bonded to a colored decorative layer detachable therefrom is usually carried out for this purpose. During the ink transfer, the substrate film is brought into mechanical contact with the raised embossed areas of the motor vehicle number plate and the decorative layer is transferred thereto under pressure, optionally also under pressure and at elevated temperature.
In order to increase the recognizability of the character legend, the support plate is generally laminated over the whole area with a retroreflective film formed in a contrasting color to the character legend. In the case of the motor vehicle number plates usual in Germany, the front of the support plates are for this purpose laminated with a white, retroreflective film, while a black decorative film is pressed onto the character legend.
Owing to the increasing requirements with respect to the forgery protection of motor vehicle number plates, the retroreflective films laminated with the support plate of a motor vehicle number plate or the decorative films have already been provided with additional security features which are not directly recognizable with the naked human eye and therefore do not impair the appearance of the motor vehicle number plate and the readability thereof. For this purpose, the security features are formed, for example, particularly small and are introduced so that they are visible only from very specific viewing angles.
Thus, DE 102 41 803 A1 discloses a blocking film with a substrate film and a decorative layer detachable therefrom for stamping a motor vehicle number plate in the area of the character legend. The blocking film is individualized by introducing security features by removing areas of the decorative layer, changing the color of said areas or bonding said areas nondetachably to the substrate film.
Such additional security features have, however, proved to be relatively easy to copy, so that there is still a need to provide a forgery-proof film for coating the character legend. In particular, the optically variable effects which are produced by one of the films mentioned at the outset, which comprise at least one transparent replicating layer having a diffractive relief structure and a reflective layer would be of particular interest as additional security features owing to their high level of protection against forgery and/or impressive decorative effect.
This applies not only to motor vehicle number plates but also to the abovementioned components in the interior of a motor vehicle, in the case of pieces of furniture, packagings and certain valuable documents such as in the area of a magnetic stripe of a bank card and the like. There is therefore generally the need for forgery-proof and/or decorative films which, for these specific applications, substantially preserve the usual appearance of the articles coated therewith.